AT697F datasheet(32/155 Pages) ATMEL

32 / 155 page

7703C–AERO–6/09

AT697F ADVANCE INFORMATION

To detect if the written address is part of a protected segment (or block), address bit 29 down to

bit 2 are Xored with the WPRx TAG. This operation is based on the following segmentation of

an address.

Table 14.

bit num. 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9

field

area

most significant byte

32Kbyte protected block

Address Segmentation

With such segmentation, memory block in the range of 32Kbyte up to 1Gbyte can be protected.

The result of the Xor is then Anded WPRx MASK.

If the result is zero, this indicates that address specified is in the protected range. If result is dif-

ferent from zero, address is out of the protected address range. If a write protection error is

detected, the write transaction is stopped. Then, a memory access error is generated. Trap

0x2B is generated

Figure 16. RAM Write Protection Overview

Write Protection Reg.

WRPn

Trap 0x2B

logic

Protection Priorities

As a result of the write protection implementation for the RAM area,the two RAM write protection

schemes can be used simultaneously. Combining the write protection schemes leads to the fol-

lowing behaviors :

•

If all the enable protection units are configured in block protect mode (BP = 0), then a write

protect error is generated when any of the units signal a write protection hit. In this mode, if

at least one protection error is triggered, the write protection trap is raised.

•

If at least one of the protection units operates in segment mode (BP=1), then a write protect

error is generated

only if all units configured in segment mode signal a protection error.

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